Referring to FIG. 1, a typical circuit 10 for driving or powering a plurality of LEDs in the prior art is illustrated. For example, the circuit 10 is used for driving 4 LEDs 22, 24, 26, and 28, as shown in FIG. 1. It will be appreciated that the LEDs 22, 24, 26, and 28 are coupled in parallel. An external voltage source is coupled to a driver 12 for supplying a voltage, Vcc, to the driver 12. The driver 12 has a low-dropout (LDO) regulator 14 for supplying a regulated voltage, Vreg, to the LEDs 22, 24, 26, and 28. Typically, the regulated voltage, Vreg, is 3.3 volts. The LEDs 22, 24, 26, and 28 are coupled to switches 32, 34, 36 and 38 and resistors 42, 44, 46, and 48, respectively. As shown in FIG. 1, the LEDs 22, 24, 26, and 28, the switches 32, 34, 36 and 38, and the resistors 42, 44, 46, and 48 are coupled in series, respectively.
For example, the current requirement for each one of the LEDs 22, 24, 26, and 28 is 10 mA. On the condition that the voltage, Vcc, of the external voltage source is 30 V, the power requirement for the LEDs 22, 24, 26, and 28 is Pw, where Pw is calculated as follows: Pw=30V×4×10 mA=1.2 W.
In a practice use, the circuit 10 may be installed in a portable device, such as a cellular phone, a digital camera, a laptop computer, electrical vehicle or portable power tool. As shown in Prior Art FIG. 1, a single high voltage integrated circuit (IC) is used, and thus only a single high voltage power supply is provided. Whether the load current is drained out of a low voltage regulator or out of a higher voltage regulator, the current flows through the IC and must dissipate a significant amount of power. This is significant from some points of view, such as, IC design, system power budget and power dissipation inside the system.